A primitive mid-Cambrian animal called Pikaia gracilens, found only in the fossil beds of Canada's Burgess Shale, is the earliest known human ancestor, according to a study published Monday in the British scientific journal Biological Reviews.
Since the first Pikaia fossils were discovered a century ago in the Burgess Shale area of the Rocky Mountains by American paleontologist Charles Walcott, the tiny, wormlike sea dweller has been the subject of ongoing debate as to its significance in human evolution.
For the study, researchers from the University of Cambridge, the Royal Ontario Museum and the University of Toronto examined 114 Pikaia fossils, 60 of which came from the ROM's exclusive collection, using a range of advanced imagery techniques, including scanning electron microscopy. For the first time, researchers were able to confirm that Pikaia not only had a notochord, which evolved into the backbone in all vertebrates, but also a vascular system, including blood vessels, as well as blocks of skeletal muscle tissue known as myomeres.
"The discovery of myomeres provides the smoking gun that we have long been seeking," said researcher and Cambridge professor Simon Conway Morris, a world-renowned Burgess Shale expert. "This study clearly places Pikaia as one of the planet's first and most primitive chordate animals – so next time we put the family photograph on the mantle-piece, there in the background will be Pikaia."
"When I was a kid thinking about my roots, I thought of Australopithecus in Africa," said Dr. Jean-Bernard Caron, the study's co-author and the curator of Invertebrate Palaeontology at the ROM. "But when you peel the onion and go deeper, Pikaia is at the bottom of the chain of events that lead to us and the rest of the vertebrates. Across millions of years his lineage continued to evolve, and one of his cousins took the torch toward us."
The confirmation of Pikaia's role in vertebrate evolution also demonstrates the ongoing importance of the Burgess Shale. In January, researchers at the ROM and Lorna O'Brien, a University of Toronto PhD student, published a study on a tulip-shaped creature named Siphusauctum that could prove to be an entirely unique species.
"We hope that with continuing explorations and field work studies around the Burgess Shale in particular, other species will be discovered in the future allowing us to refine our understanding of the early history of our own group," said Dr. Caron.